"Look at this fish, wow, look at those eyes, look at those eyes," he remembered thinking.
"I was nine feet away from it and it was checking me out as much as I was checking it out," he said. "It was cool, it was wild, I was loving every minute of it.
Macallister was taking a video six miles off the coast of Provincetown.
"I was perfectly comfortable there," he said.
He continued to film the video while suspended above the shark on the pulpit of his boat - similar to when he harpoons tuna fish.
"The shark was just calm. It was just checking us out," he said. "It would go up a little bit, it would go down a couple of times."
That continued for about 10 minutes as the often-feared creature spent time swimming around the boat. But the shark, Macallister noted in the video, had absolutely no fear of the boat or its occupants.
Greg Skomal, senior scientist at the state's Division of Marine Fisheries, said there have been 39 Great Whites that have been tagged on the cape in the last five years, several of which are the same size as the one Macallister saw Monday, roughly 16 to 18 feet long.
"These white sharks do occur here this time of year so not all that surprising to me," he said.
So while the sighting was alarming to Macallister, news of the sighting wasn't out of the ordinary for scientists, and they say it shouldn't be for those who are Cape-bound, either.
"If I were coming to the Cape for the fourth of July I wouldn't be thinking about the sharks," Skomal said. "I'd be more concerned about the traffic."
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